Reduction of interlayer Co2+ ions in fluorine mica using diethylene glycol

Reduction of interlayer Co²⁺ ions in expandable fluorine mica has been attempted. The polyol process using diethylene glycol as a reducing agent was employed. The co²⁺ -exchanged mica was refluxed at about 225–235 °C in liquid diethylene glycol for 10–120 minutes. Consequently, zero-valence Co metal (Co⁰) intercalated mica having a metallic grey colour was obtained by in situ reduction of interlayer Co²⁺ ions, showing different properties from Co²⁺ -exchanged mica as a precursor. The layer charge of Co-metal-intercalated mica is compensated by protons which are produced through the course of reduction of interlayer Co²⁺ ions. The reduced sample heated at 350 °C, which had no organic molecules, exhibited a basal spacing of 1.28 nm, indicating the presence of 0.34 nm cobalt metal clusters after subtracting the thickness of the host silicate layer. During the process of reduction in diethylene glycol, cobalt metal particles were expelled from the interlayers which grew to about 0.5 m onto the external surfaces of host mica crystals with increasing refluxing time.     

Effects of particle size on thermal durability and microporous characteristics for sintered bodies of alumina-pillared fluorine micas

Powder compacts of alumina-pillared fluorine micas having different particle sizes were fired at various temperatures in the range of 500–800 °C. Sintered bodies of the alumina-pillared micas were obtained at 500–700 °C with retaining their pillared structure. The pillared structure collapsed at 800 °C, losing microporous characters. Specific surface area and micropore volume of the sintered bodies obtained from coarse particles are larger than those obtained from fine particles. Thermal durability of the pillared structure depends on the particle size of alumina-pillared fluorine micas, especially on the c-dimension of the host mica crystals; thermal durability of the sintered bodies obtained from coarse particles is higher than that from fine particles. The sintered bodies are machinable due to the interlocking microstructure of the flaky mica crystals.     

Grinding effects of host crystals on formation and properties of titania pillared fluorine micas

Fluorine micas having different grinding times were allowed to react with titania sol prepared by hydrolyzing titanium tetraisopropoxide (TTIP) with hydrochloric acid in order to clarify the influence of grinding upon reactivity of synthetic fluorine micas [M_0.8Mg_2.2Li_0.8(Si₄O₁₀)F₂(M = Na, Li)]. Prolongation of grinding time promoted delamination and fineness of host mica crystals, resulting in increasing specific surface area. The heating weight loss and intensity of IR absorption bands around 1600 and 3400 cm^–1 also increased with increasing grinding time, indicating the increase in absorbed water on ground mica particles. Properties of titania pillared fluorine micas depended on grinding time of host micas. Specific surface areas and titania contents of pillared fluorine micas increased with increasing grinding time, so that the effect of interlayer cations (Na⁺, Li⁺) upon complex formation of titania pillared micas almost diminished. When host mica crystals were larger, the reaction occurred mainly in the interlayer region. However, when host mica crystals were ground to be finer, the reaction on external surfaces of ground particles occurred simultaneously along with intercalation. These results show that mechanochemical effects resulted from grinding have the profound influence on the formation and properties of titania pillared fluorine micas.     

Colorimetric and fluorescent sensing of transition metal ions in aqueous medium by salicylaldimine based chemosensor

The cation sensing property of highly sensitive chromogenic receptor N, N′-bis (salicylidine)-o-phenylene diamine (receptor 1) was studied by visual observation, UV–vis spectroscopy and fluorescence spectroscopy. The proposed study has been targeted to sense the first transition series metal cations like Fe³⁺, Co²⁺, Ni²⁺ and Cu²⁺. Binding affinity toward Cu²⁺ is found to be of higher magnitude compared to the other three cations mentioned. Receptor 1 on binding with Fe³⁺, Co²⁺ Ni²⁺ and Cu²⁺ ions shows fluorescence enhancement which is due to the inhibition of PET mechanism.     

Metal clusters and nanoparticles assembled in zeolites: an example of stable materials with controllable particle size

An ion-exchangeable zeolite (mordenite) is used to control the formation of nanoparticles and clusters within the solid matrix by the hydrogen reduction of metal ions (Ag⁺, Cu²⁺, and Ni²⁺). SiO₂/Al₂O₃ molar ratio in mordenite appears to be an efficient tool to manage the reducibility of the metal ions. Few-atomic silver clusters in line with the larger silver nanoparticles were observed with DRS for the reduced Ag⁺-exchanged mordenites. Cu²⁺-exchanged ones produce the copper nanoparticles with different optical appearance, and Ni²⁺-exchanged mordenites are reduced up to complicated species with no explicit assignment of metal particles under the conditions studied.     

Synthesis of spherical nanostructured LiMxMn2−xO4 (M = Ni, Co, and Ti; 0 ≤ x ≤ 0.2) via a single-step ultrasonic spray pyrolysis method and their high rate charge-discharge performances

LiM_xMn_2−xO₄ (M = Ni²⁺, Co³⁺, and Ti⁴⁺; 0 ≤ x ≤ 0.2) spinels were prepared via a single-step ultrasonic spray pyrolysis method. Comparative studies on powder properties and high rate charge-discharge electrochemical performances (from 1 to 15 C) were performed. XRD identified that pure spinel phase was obtained and M was successfully substituted for Mn in spinel lattice. SEM and TEM studies confirmed that powders had a feature of ‘spherical nanostructural’, that is, powders consisted of spherical secondary particles with the size of about 1 μm, which were developed from close-packed primary particles with several tens of nanometers. Substitutions enhanced density of second particles to different extents, depending on M and its content. Charge-discharge tests showed that as-prepared LiMn₂O₄ could deliver excellent rate performance (around 100 mAh/g at 10 C). Ni substitution contributed to improving electrochemical performances. In the voltage range of 4.95-3.5 V, the materials showed much better electrochemical performances than LiMn₂O₄ in terms of capacity, cycleability and rate capability.     

Solid-state synthesis and electrical properties of polyaniline/Cu-montmorillonite nanocomposite

In this paper, the solid-state synthesis of polyaniline/Cu-montmorillonite nanocomposite is reported. Mixture of anilinium chlorure and Cu exchanged montmorillonite was grinded at room temperature while we vary the molar rate of aniline to interlayer Cu²⁺ cations (R) from 0.5 to 6. The properties of the hybrid compounds are characterized by X-ray diffraction, thermogravimetric analysis, SEM, FTIR and impedance spectroscopy. The results showed that the structure and the conductivity of PANI in hybrid materials depend on R. The ac conduction showed a regime of constant dc conductivity at low frequencies and a crossover to a frequency-dependent regime of the type A ω^s at high frequencies.     

Influence of spectator ions on the reactivity of divalent metal salts in molten alkali metal nitrates: Morphology of the resulting metal oxides

This work focuses on the investigation of the reaction of alkali metal nitrates (LiNO₃, NaNO₃ and KNO₃) with divalent metal salts (Cu²⁺, Ni²⁺ and Zn²⁺). Thermogravimetric analysis (TGA) was employed to study the kinetics and mechanisms of the above reactions, which led to the formation of the corresponding metal oxides. The reaction temperature was found to depend not only on the alkali metal but also on the metal salt (MCl₂ or M(NO₃)₂) involved in the reaction.SEM observations show that the spectator ions present in the reacting medium have varying degrees of influence on the morphology of the powder; the growth directions, sizes and the homogeneity of their distribution, are modified. KNO₃ generates the most significant differences compared to LiNO₃ and NaNO₃.     

Electron beam induced structural evolution in Fe3O4\SiO2 particles: A new route to obtain movable core structures

SiO₂ hollow spheres with movable Fe₃O₄ core were obtained by exposing the pre-synthesized Fe₃O₄\SiO₂ particles (with an adsorption interlayer of ethylene glycol) under the irradiation of electron beam inside transmission electron micrograph (TEM). In the formation process, the evaporation of adsorbed ethylene glycol and the evolution of amorphous SiO₂ layer played important roles, and that should be attributed to the high temperature and trapped charges induced by the irradiation of electron beam. This work provided a new route to obtain particles with movable core structure and extended the applications of electron beam.     

Preparation and intercalation chemistry of magnesium-iron(III) layered double hydroxides containing exchangeable interlayer chloride and nitrate ions

Layered double hydroxides (LDHs) with Mg²⁺ and Fe³⁺ cations in the brucite-like layers and having chloride or nitrate ions in the interlayer region have been prepared and characterized by powder X-ray diffraction (PXRD), elemental analysis and thermal analysis. Thermal decomposition of the LDH-nitrate occurs in two steps, with loss of water followed by simultaneous dehydroxylation of the layers and loss of NO_x/O₂ arising from the nitrate anions. Thermal decomposition of the LDH-chloride involves an additional step, with chloride ions becoming grafted to the layers, prior to loss of HCl. The interlayer anions may be readily replaced by sulfate, thiosulfate, tartrate and vinylbenzenesulfonate ions suggesting that these materials may be useful precursors to Mg-Fe(III) LDHs intercalated with a variety of inorganic and organic anions.     

Intercalation of polyethylene oxide PEO in layered MPS3 (M = Ni, Fe) materials

The intercalation compounds Li_0.96(H₂O)_0.77(PEO)_0.63Ni_0.48PS₃ and Li_0.94(H₂O)_0.92(PEO)_0.94Fe_0.48PS₃ obtained by the insertion of PEO in MPS₃ form lithium-polyethylene oxide complexes containing Li⁺ exchangeable cation in the interlayer space. Polyethylene oxide (PEO) is able to associate interlayer cation increasing the ionic conductivity of NiPS₃ and FePS_3. These compounds constitute a new family of intercalates MPS₃ (M = Ni, Fe) host-layer materials.The new materials were characterized by powder X-Ray diffraction (XRD), Fourier-transformed infrared (FT-IR), differential thermal and thermogravimetric analyses (DTA/TG), energy dispersive X-Ray (EDX), inductively coupled plasma (ICP) and electrochemical impedance measurements. The intercalation compound Li_0.96(H₂O)_0.77(PEO)_0.63Ni_0.48PS₃ shows an ionic conductivity of 0.13 μS/cm, and dc electronic conductivity of ca. 0.1 μS/cm which is twice that of NiPS₃.     

Synthesis and characterization of Ni1−xZnxFe2O4 spinel ferrites from tailored layered double hydroxide precursors

In this paper, a series of pure Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrites have been synthesized successfully using a novel route through calcination of tailored hydrotalcite-like layered double hydroxide molecular precursors of the type [(Ni + Zn)_{1 − x − y}Fe_y²⁺Fe_x³⁺(OH)₂]^x+(SO₄²⁻)_x/2·mH₂O at 900 °C for 2 h, in which the molar ratio of (Ni²⁺ + Zn²⁺)/(Fe²⁺ + Fe³⁺) was adjusted to the same value as that in single spinel ferrite itself. The physico-chemical characteristics of the LDHs and their resulting calcined products were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy. The results indicate that calcination of the as-synthesized LDH precursor affords a pure single Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrite phase. Moreover, formation of pure ferrites starting from LDHs precursors requires a much lower temperature and shorter time, leading to a lower chance of side-reactions occurring, because all metal cations on the brucite-like layers of LDHs can be uniformly distributed at an atomic level.     

The effect of Cu content on the structure of Ni1−xCuxFe2O4 spinels

A series of Ni_1−xCu_xFe₂O₄ (0 ≤ x ≤ 0.5) spinels were synthesized employing sol-gel combustion method at 400 °C. The decomposition process was monitored by thermal analysis, and the synthesized nanocrystallites were characterized by X-ray diffraction, transmission electron microscopy, infra-red and X-ray photoelectron spectroscopy. The decomposition process and ferritization occur simultaneously over the temperature range from 280 °C to 350 °C. TEM indicates the increase of lattice parameter and particle size with the increase of copper content in accordance with the XRD analysis. Cu²⁺ can enter the cubic spinel phase and occupy preferentially the B-sites within x = 0.3, and redundant copper forms CuO phase separately. A broadening of the O 1s region increases with the increment of copper content compared to pure NiFe₂O₄, showing different surface oxygen species from the spinel and CuO. Cu²⁺ substitution favors the occupancy of A-sites by Fe³⁺.     

Effect of layer charge on chemical and physical properties of synthetic K-fluorine micas

The fluorine micas (K-fluorine micas; K_XMg_3-XLi_XSi₄O₁₀F₂) having variable layer charges (x = 0.4–1.0) were synthesized. The lattice constant c decreased with a decrease in the layer charge while the lattice constants a and b increased. As the layer charge decreased, K-fluorine micas were changed into Na-fluorine micas more rapidly by NaB(C₆H₅)₄ treatment and were easier to cleave and change into the amorphous phase by grinding. The mica ceramics with lower layer charges showed lower electrical resistance than those with higher layer charges in the low-temperature region but higher electrical resistance in the high-temperature region. The results of the electrical resistance can be explained by the concentrations of the lattice vacancy and K⁺ ion in the interlayer. The dielectric loss tangent was influenced by the layer charge while the dielectric constant was almost unchanged. The chemical and physical properties of such micas are strongly dependent on the magnitude of the layer charge because the layer charge determines the interlayer bonding strength and the stability of mica structure.     

Mesoporous nickel (or cobolt)-doped silica-pillared clay: Synthesis and characterization studies

The metals-doped silica-pillared clay (SPC) materials with ordered pore structure in the gallery were obtained by a surfactant-directed assembly of silica species in the interlayer space of natural montmorillonite (MMT). The novel method afforded SPC derivatives with basal spacings of 4.4-4.5 nm, BET specific surface areas of 382.4-472.6 m²/g, pore volumes of 0.64-0.71 cm³ g⁻¹ and uniform pores (3.6 nm) between the layers. The main nickel and cobalt species was tetrahedrally coordinated Ni²⁺ or Co²⁺ in the gallery silica framework. Our results indicate that surfactant plays a decisive role in pore formation, because in acts as a micelle-like template during the hydrolysis of TEOS. In particular, the formation of metal-ammonia complex and rapid adsorption by surfactant in galleries controls metal species outflow from interlayers and contributes to the formation of metal species containing firm silica-pillars.     

Synthesis of layered Li1.2+x[Ni0.25Mn0.75]0.8−xO2 materials (0 ≤ x ≤ 4/55) via a new simple microwave heating method and their electrochemical properties

Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55) was prepared by a new simple microwave heating method and the effect of extra Li⁺ content on electrochemistry of Li_1.2Ni_0.2Mn_0.6O₂ (x = 0) was firstly revealed. X-ray diffraction identified that they had layered α-NaFeO₂ structure (space group R-3m). Linear variation of lattice constant as a function of x value supported the formation of solid solution, that is, extra Li⁺ is possibly incorporated in structure of layered Li_1.2Ni_0.2Mn_0.6O₂ (x = 0), accompanying oxidization of Ni²⁺ to Ni³⁺ to form Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55). This was confirmed by X-ray photoelectron spectroscopy that Ni³⁺ appeared and increased in content with increasing x value. Charge–discharge tests showed that Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55) truly displayed different electrochemical properties (different initial charge–discharge plots, capacities and cycleability). Li_1.2Ni_0.2Mn_0.6O₂ (x = 0) in this work delivered the highest discharge capacity of 219 mAh g⁻¹ between 4.8 and 2.0 V. Increasing Li content (x value in Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂) reduced charge–discharge capacities, but significantly enhancing cycleability.     

Synthesis and characterization of crystalline hexagonal bipods of zinc oxide

The preparation of nano- and submicrometre-sized one-dimensional (1D) zinc oxides (ZnOs) from zinc nitrate was performed by precipitation with urea in two types of solvents (water and water/polyol mixtures). The influence of different polyols (ethylene glycol, diethylene glycol and tetraethylene glycol) on the size of the final particles (length and diameter) is presented for the first time. As well as the influence of the solvents used, the ratio of water/polyol, temperature, pH and time of synthesis was correlated with the size and morphology of the final particles. In all cases crystalline ZnO was synthesized in the form of hexagonal bipods. The morphological and crystalline properties of the samples obtained were characterized by SEM, IR, and XRD.     

Inorganic phosphate crystal Na15−n[Al(PO4)2F2]3−n[Ti(PO4)2F2]n (0 ≤ n < 1): A novel cation exchanger with high exchange selectivity for Li and Pb ions

A series of inorganic phosphate crystals have been hydrothermally synthesized, which have high chemical stability and can keep their crystal structure after acid/base treatments. Its cation-exchange properties have been investigated and the results show that it is an excellent ion exchanger with high exchange capacities for H⁺, Li⁺ and Pb²⁺ ions (12.74, 6.98 and 3.92 mequiv./g, respectively). Selective extractions of Li⁺ and Pb²⁺ from the synthetic mixtures containing (Li⁺, Sr⁺, K⁺, Mg²⁺, Ca²⁺ and Ba²⁺) and (Pb²⁺, Ca²⁺, Ba²⁺, Co²⁺, Ni²⁺, Zn²⁺ and Mg²⁺) have been observed. The reasons of the high exchange selection of NATP for Li⁺ and Pb²⁺ ions have been discussed.     

X-ray Rietveld analysis and Fourier transform infrared spectra of the solid solutions [Eu2−xMx][Sn2−xMx]O7−3x/2 (M = Mg or Zn)

Two series of mixed oxides with formula [Eu_2−xM_x][Sn_2−xM_x]O_7−3x/2 (M = Mg or Zn) have been synthesized. The study by X-ray diffraction and Fourier transform infrared spectroscopy shows that the solids obtained are new non-stoichiometric solid solutions with the pyrochlore type structure. For both series a decrease of the cell parameter is observed when the degree of substitution, x, increases. The structural refinements (X-ray studies) were achieved in the space group Fd-3m, no. 227 (origin at center -3m) by using the Fullprof software. The Rietveld refinements show that the divalent cations M²⁺ (Mg²⁺, Zn²⁺) substitute isomorphically for Eu³⁺ and Sn⁴⁺ ions producing vacancies in the anionic sublattice.     

Studies on divalent ion uptake of transition metal cations by calcite through crystallization and cation exchange process

The uptake of transition metal cations of Fe, Cu, Zn, Cd and Pb with calcium carbonate in the form of calcite was investigated. The uptake reaction was found to be in the following order: Pb²⁺ > Cu²⁺ Zn²⁺ > Cd²⁺ Fe²⁺; and the amount of uptake (meq/g) cations has been found to increase with the increase of the metal ion concentration and reaction time. The uptake of these ions was mainly considered to be due to the crystallization that happens through decomposition reaction mechanism as in case of Pb²⁺, Cu²⁺ and Zn²⁺ and cation exchange of surface Ca²⁺-ions present in lattice structure of carbonate solid with metal cations, as in the case of Fe²⁺ and Cd²⁺. The different affinities of calcite toward these cations can be used for waste ions fixations or decontamination.